Related Clues:

• Geological span
• Geologic divisions
• History unit
• Major time periods
• Loooong time
• It's comprised of ages and ages
• An extremely long time
• Heck of a long time
• Really big span
• Years and years on end
• Unimaginably long time
• Long time division
• Long times to wait
• Geological time span
• Span longer than an era